1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method. More specifically, the invention relates to a lithographic apparatus that includes a movable carriage for moving an article support member.
2. Description of Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. including part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to this direction.
In conventional structures for moving and supporting the article support member, in particular, a wafer table for supporting a wafer to be irradiated by a radiation beam of the lithographic apparatus, or, a mask table for supporting a mask defining a circuit pattern, due to the extreme accurate positioning requirements, a carriage structure is used wherein the mechanical stiffness properties are optimal. Furthermore, due to the heat generated by the actuators for moving the carriage, and radiation received on the structure to be irradiated, a substantial need exists to provide cooling in the carriage structure. To this end, conventional materials like aluminum and titanium are used which are cooled by cooling circuits integrated in the structure. One problem related to the cooling and stiffness requirements of the carriage is that the options to provide further reduction of the weight thereof are rather limited, since there are minimum thicknesses to be observed for the carriage in order to maintain sufficient mechanical integrity. Such cooling is essential for these conventional materials, since slight temperature variations can result in unacceptable contracting or expanding of the material. Even a temperature fluctuation as little as 2° K can cause sensors that are arranged for driving actuators for actuating the carriage to be displaced over a distance to be out of tolerance for placing the substrate on a predetermined position.